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Nowadays, the advent of pressure sensors for intelligence terminal devices and skin‐inspired electronics has trigged rapid development of flexible, sensitive, and transparent sensing materials. Piezo‐active poly(vinylidene fluoride) (PVDF) is emerging as a promising candidate for sensing components due to the flexible and transparent features. However, the inherent weak piezo‐activity and consequently low sensitivity of PVDF remains a challenge for its sensing applications. Herein, ionic liquids ([EMIM]Cl) additive combined with a composition‐gradient multilayered architecture design are employed to hardness the piezo‐response of PVDF. The resultant composites present ultra‐high piezoelectric coefficient d33 of 39 pC N−1, which is 2.78 times that of PVDF. Meanwhile, the transparent ILs dopant enables the composites with superior transparency (87%). With notable advantages of high transparency and piezoelectricity, the ILs/PVDF composites exhibit high sensitivity of 0.0423 V N−1, ultra‐fast recovery time of 0.2 ms and stable operation capability when coupled with metal electrodes, confirming their applicability for reliable pressure sensor. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The harvester can scavenge energy from ultra-low frequency vibrations. • The harvester can capture vibration energy from any direction. • The harvester can up-convert the excitation frequency through internal resonance. • The harvester is designed with a novel piezoelectric spring based on binder clips. • A significant generated power of 13.29 mW (at 0.26 g, 2.03 Hz) is obtained. Abstract Low frequency vibration is a ubiquitous energy existing in our environment, but a large efficient harvesting of which remains challenging. This paper presents a simple piezoelectric spring architecture based on a common binder clip structure. The harvester with pendulum spring allows the energy of the dynamic mass to be converted into electrical energy in the piezoelectric transducer. Due to the basic characteristics of spring pendulums, the proposed harvester can efficiently scavenge not only ultra-low frequency but also multi-directional vibrational energies. Modeling and design are conducted and a normalized expression of the harvester behavior is given. Chirp and human motion excitations are used to evaluate the proposed harvester's performances. Simulation and experimental results are in good agreement. The proposed device could generate a high output power (13.29 mW) at a low operating frequency (2.03 Hz), which shows great application prospects in the power supply of wearable products, ocean buoys, etc. [ABSTRACT FROM AUTHOR]

Abstract: In the paper, a vibration damping system powered by harvested energy with implementation of the so-called SSDV (synchronized switch damping on voltage source) technique is designed and investigated. In the semi-passive approach, the piezoelectric element is intermittently switched from open-circuit to specific impedance synchronously with the structural vibration. Due to this switching procedure, a phase difference appears between the strain induced by vibration and the resulting voltage, thus creating energy dissipation. By supplying the energy collected from the piezoelectric materials to the switching circuit, a new low-power device using the SSDV technique is proposed. Compared with the original self-powered SSDI (synchronized switch damping on inductor), such a device can significantly improve its performance of vibration control. Its effectiveness in the single-mode resonant damping of a composite beam is validated by the experimental results. [Copyright &y& Elsevier]

The energy conversion efficiency (ECE) of a piezoelectric generator can be denoted by its effective electromechanical coupling coefficient (EECC), which depends only on the geometry parameters with a certain boundary conditions. To obtain the optimal energy-harvesting device, the Raleigh Method was utilized to establish the analysis model of circular piezoelectric composite diaphragms. Simply supported and clamped boundary conditions were considered. The relationships between the performance parameters (EECC and natural frequency) and the structural parameters (diametric ratio β and thickness ratio α) of piezoelectric composite diaphragms were figured out. Given the correlative material parameters and boundary conditions, the performance parameters with the structural parameters as variables can be worked out. The simulation results show that the optimal structural parameters of a composite diaphragm in the case of the simply supported and clamped boundary conditions are different. A simply supported diaphragm generator tends to achieve higher effective electromechanical coupling coefficient and lower natural frequency, and is more suitable for the applications of energy harvesting. [ABSTRACT FROM AUTHOR]

• A novel synchronized switch damping technique based on energy injection strategy is proposed. • The injection energy can be easily adjusted through changing the duty cycle of the corresponding switch control signal. • Low voltage source might lead to high piezoelectric driven voltage in the proposed technique. • Piezoelectric structural damping characteristic can be effectively enhanced or timely adjusted. • The stability problem of the controlled system can be easily solved and implemented. Synchronized switch damping (SSD) principle and derived techniques are a classical semi-active vibration control method based on piezoelectric elements. This paper presents a novel energy injection based SSD technique which has better effect of vibration reduction but with simpler implementation of electronic circuitry. The proposed circuit is composed of a flyback transformer, an ordinary low voltage source and two kinds of synchronized switches. Through controlling the synchronized switches, the electrical energy is extracted from the voltage source to the transformer, and then injected to the piezoelectric elements, increasing the piezoelectric voltage as needed. Moreover, this injection energy can be easily adjusted by changing the duty cycle of the corresponding switch control signal. The operation principle of this technique is introduced, the analytical expression of vibration attenuations is also derived for a typical electromechanical model. Finally, theoretical predictions confirmed by experimental results show that the proposed SSD technique provides an adaptive structural damping and enhances the effect of vibration attenuation. [ABSTRACT FROM AUTHOR]

• The two-dimensional MXene nanosheet demonstrates to be novel effective reinforcement for piezoelectric PVDF polymer. • Upon a small loading of 0.4 wt.%, the piezoelectric coefficient d 33 of MXene/ PVDF hybrid film reach the peak of 43 pC/N. • The sensor based on MXene/ PVDF hybrid film perform superior voltage sensitivity up to 0.0480 V/N. The rapid advances in intelligence terminal devices have raised expectations for highly sensitive, reliable and flexible pressure sensor. Herein, we present a highly sensitive flexible pressure sensor based on piezoelectric MXene/poly(vinylidene fluoride) (PVDF) hybrid film. Making use of MXene nanosheet reinforcement, one can efficiently promote the piezoelectric output and consequently sensitivity of PVDF. For instance, upon a small loading of 0.4 wt%, the piezoelectric coefficient d 33 of MXene/PVDF hybrid film reaches the peak of 43 pC/N. Meanwhile, the incorporation of MXene nanosheet is advantageous to strengthen the mechanical performance of PVDF. With the excellent piezoelectric response and mechanical property, the MXene/PVDF hybrid film sensor demonstrates to perform superior voltage sensitivity up to 0.0480 V/N, which is double that of PVDF based sensor. Meanwhile, the novel hybrid film sensor also exhibits fast recovery time of 3.1 ms and stable operation capability under cyclic force, confirming their applicability as reliable pressure sensor. [ABSTRACT FROM AUTHOR]